The present invention relates to a process for the preparation of naphthalene or a derivative thereof. More particularly, the present invention relates to an improvement of the process for preparing naphthalene or a derivative thereof by means of cyclodehydrogenation of a benzene derivative having at least one aliphatic hydrocarbon group.
For the preparation of naphthalene or a derivative thereof, a process is known in which a benzene derivative having at an appropriate position an aliphatic hydrocarbon group as a side chain with an appropriate carbon chain length and being capable of forming naphthalene or a derivative thereof is subjected to cyclodehydrogenation by using a catalyst wherein a noble metal such as platinum, palladium, etc., is carried on alumina or the like, to obtain the naphthalene or the derivative thereof of a corresponding structure (for example, Japanese Patent Publication (Kokoku) No. 52-47460 (1977)).
However, when the above-mentioned catalyst is used in the cyclodehydrogenation process, the cyclization yield is unsatisfactory and the cyclic hydrocarbons of a 5-member ring such as alkylindane or alkylindene having the same total number of carbon atoms as naphthalene or a derivative thereof obtained therefrom are formed as by-products. These by-products are difficult to separate from naphthalene or a derivative thereof, as their boiling point is close to that of naphthalene or a derivative thereof, so that it is difficult to obtain the objective product with high purity.
There is also known a process for preparing dimethylnaphthalene by using a chromium oxide-aluminum oxide based catalyst (Japanese Patent Application Laid-Open (Kokai) No. 49-62453(1974)). However, when this catalyst is used, the selectivity of dimethylnaphthalene or the conversion ratio of the starting material is unsatisfactory.
Recently, a catalyst composed of zirconia and an alkaline earth metal oxide has been proposed, and attention is drawn to its remarkably high naphthalene selectivity in comparison with the conventional noble metal carrying-type catalysts or chromium oxide-aluminum oxide based catalysts (Japanese Patent Application Laid-Open (Kokai) No. 62-240631(1987)).
According to the studies by the present inventors, however, the catalyst disclosed in Japanese Patent Application Laid-Open (Kokai) No. 62-240631 was still not well satisfactory and needed further improvement in respect of selectivity, too.
Naphthalene or a derivative thereof is industrially used in great quantities as, for example, a base material of polymers used as industrial materials. Therefore, as the preparation method of naphthalene or a derivative thereof, there is mostly employed a continuous reaction system which is suited for mass production of the intended substance. In the continuous reaction system, the difference in conversion and selectivity in one cycle of reaction greatly affects the yield of the intended product after a long-time continuous operation. Therefore, development of a process which is higher in conversion ratio and selectivity as much as possible, even by a few percent, than the conventional methods has been strongly desired.
As a result of strenuous studies for attaining the above requirement, it has been found that by using a zirconia catalyst containing chromium in an oxidized state, naphthalene or a derivative thereof can be obtained efficiently with a high conversion ratio and a high selectivity from a benzene derivative having at least one aliphatic hydrocarbon group as a side chain and being capable of forming a naphthalene ring. On the basis of this finding, the present invention has been attained.